The invention relates to a ram boring device for creating horizontal boreholes and to a method for operating a corresponding ram boring device.
Ram boring devices of this type are known in the art and are used, in particular, to create horizontal boreholes in the ground. Typically, such ram boring device has an impact piston which moves in an oscillatory fashion (back and forth) inside the casing and thereby strikes a front or rear impact face of the casing depending on the desired movement direction of the ram boring device. The transferred kinetic energy of the impact piston causes an acceleration of the ram boring device in the soil.
Such ram boring device is disclosed, for example, in U.S. Pat. No. 5,148,878 A. The ram boring device disclosed therein includes a control tube which movably supports an impact piston. The rear end of the control tube is fixedly connected with a compressed air supply; the control tube is also connected via a pretensioned coil spring with a component affixed to the housing to enable both longitudinal axial and rotational movement. The spring force urges the control tube into a forward position (advance position) and locks the control tube in this position by a quarter turn in a locking groove. The device is reversed by unlocking the control tube by rotating the compressed air supply by a quarter turn against the spring bias, whereby the control tube is moved into a rear position (return position) by the effect of the compressed air and opposite the longitudinal axial spring force. At the same time, the center position of the impact piston is displaced inside the casing, causing the impact piston to strike a rear impact face in the return position. Like in the forward position, the control tube is in the return position locked in a second locking groove through the effect of the rotationally-biased spring. With another quarter turn of the control tube, the ram boring device is again reversed into the advance position, wherein the level of the pressure of the supplied compressed air is simultaneously reduced, causing the forces produced by the pretensioned spring to exceed the pressure forces and thus moving the control tube again into the forward position.
The device in U.S. Pat. No. 5,148,878 A thus discloses two operating positions, in which either a front or a rear impact face of the casing is struck.
It is the object of the invention to improve a ram boring device so that the impact frequency and/or the impact intensity can be influenced.